The Nigerian terrorist group Boko Haram has reportedly released a new video message in which they show some of the hundreds of schoolgirls they have kidnapped, and offered to release them in exchange for prisoners.

Abubakar Shekau, the leader of the militant group, also said that the girls had been converted to Islam while in captivity.

A woman demands the release of the abducted school girls, during a protest in in the Nigerian capital of Abuja. Photo: Joe PenneyActivists pause during a prayer vigil for abducted Nigerian schoolgirls in front of the Consulate General of Nigeria in Manhattan, New York MayA man shouts "Bring back our girls," ahead of a prayer vigil for abducted Nigerian schoolgirls outside the Consulate General of Nigeria in Manhattan, New YorkA boy takes part in a prayer vigil for abducted Nigerian schoolgirls in front of the Consulate General of Nigeria in Manhattan,A woman prays for the release of secondary school girls abducted from in the remote village of Chibok, at an Evangelical Church of West Africa (ECWA) church in Abuja MayPeople demand for the release of 200 secondary school girls abducted in the remote village of Chibok, during a protest at Unity Park in Abuja

Shekau has previously spoken about the abduction in other filmed messages, where he appeared in military fatigues and flanked by armoured vehicles.

Today the news agency Agence France-Presse said it had seen a 17-minute video which showed around 100 girls wearing full veils praying in an undisclosed location.

Three of the girls were reported to be shown speaking in the video, in which one of them said they have not been harmed.

Two girls reportedly said they were Christian and have converted to Islam and the third said she is a Muslim.

In a separate part of the video, Shekau said that the girls would remain captive until the Nigerian government releases all imprisoned Boko Haram militants.

There are concerns that the girls may now have been split up into a number of groups, and that some may even have been smuggled out of the country altogether.

The Nigerian government has previously said it will not "pay a ransom" to get the girls back for fear that it will simply encourage further abductions in the future. The Nigerian president Goodluck Jonathan vowed on Thursday to make the incident "the beginning of the end" for terrorism in his country.

Speaking to Sky News, the father of one of the kidnapped girls said he did not want the government to accept Boko Haram's offer of an exchange for prisoners.

A girl wearing the full-length hijab appears clearly under duress as she speaks to the camera in the Boko Haram video (AFP)

"It's not right," hes said. "They'll do it again."

Though reports vary on the exact number of schoolgirls taken by Boko Haram initially, it is believed that 276 remain missing from the more than 300 kidnapped on 14 April from Chibok in the state of Borno, which has a large Christian community.

A number of the girls were able to break free from the group, and speaking yesterday one of them said more would have escaped had they not feared being shot by their captors.

The government’s failure to rescue the remaining girls has attracted mounting outrage. Last week, Nigerian president Goodluck Jonathan accepted international help after ignoring earlier offers.

The team expected in Nigeria to assist in search and rescue efforts will include US hostage negotiators, counter-terror experts and intelligence agents from Britain, France, China and Spain. Israel also offered assistance on Sunday.

A screengrab from the video released by Boko Haram shows a man claiming to be their leader, Abubakar Shekau (AFP)

Around the world, the effort to rescue the captives has been fuelled by a social media campaign, under the hashtag #BringBackOurGirls. Yesterday it was joined by the Prime Minister, David Cameron, who later came in for criticism that there were more practical things he could do to help.